1. Field of the Invention
The present invention relates to a method and an apparatus for plating a substrate. More particularly, it relates to a method and an apparatus for plating a substrate such as a semiconductor wafer to fill a metal such as copper (Cu) or the like in interconnection grooves defined in the substrate.
2. Description of the Related Art
In recent years, there has been a growing tendency to use copper, which has low electric resistivity and high electromigration resistance, instead of aluminum or aluminum alloy, as a metal material for forming interconnection circuits on semiconductor substrates. Copper interconnections are generally formed by filling copper in minute grooves or recesses defined in the surface of a semiconductor substrate. Specifically, copper interconnections are formed by depositing a film of copper over the entire surface of the semiconductor substrate according to CVD, sputtering, or plating, and then removing unwanted copper from the surface according to a chemical mechanical polishing (CMP) process, leaving copper in the grooves or recesses.
FIGS. 28A through 28C of the accompanying drawings show successive steps of manufacturing a substrate W with copper interconnections. As shown in FIG. 28A, an oxide film 2 of SiO2 is deposited on a conductive layer 1a on a semiconductor substrate 1 on which semiconductor devices are formed. Then, a contact hole 3 and an interconnection groove 4 are formed in the oxide film 2 by lithography and etching. Thereafter, a barrier layer 5 of TiN or the like and a seed layer 7 as a layer for supplying an electric current for electroplating are successively formed on the surface formed so far.
Then, as shown in FIG. 28B, the entire surface of the substrate W is plated with copper to deposit a copper layer 6 on the entire surface, filling the contact hole 3 and the groove 4 with copper. Thereafter, the copper layer 6 over the oxide film 2 is removed by CMP, making the copper layer 6 in the contact hole 3 and the groove 4 lie flush with the oxide film 2. In this manner, an interconnection made of the copper layer 6 is produced as shown in FIG. 28C.
FIG. 29 of the accompanying drawings shows a conventional general arrangement of a cup type apparatus of the face-down type. The cup type plating apparatus has a cylindrical plating chamber 12 which is open upwardly and holds a plating solution 10 therein, and a substrate holder 14 for removably holding a substrate W such as a semiconductor wafer downwardly and positioning the substrate W in a position close to the upper open end of the plating chamber 12. The plating chamber 12 houses therein a planar anode plate 16 immersed approximately horizontally in the plating solution 10. The substrate W serves as a cathode. The anode plate 16 is made of a porous material or a mesh material.
A plating solution ejector pipe 18 for producing an upward jet of plating solution is connected centrally to the bottom of the plating chamber 12. The plating chamber 12 is surrounded by a plating solution reservoir 20 positioned around an upper portion of the plating chamber 12. The plating solution ejector pipe 18 is connected to a plating solution supply pipe 28 that extends from a plating solution storage tank 22 and has a pump 24 and a filter 26. The plating solution storage tank 22 is connected to a plating solution return pipe 30 extending from the plating solution reservoir 20.
The substrate W is held above the plating chamber 12 by the substrate holder 14. The surface to be plated of the substrate W faces downwardly. While a predetermined voltage is being applied between the anode plate 16 and the substrate W, the plating solution 10 in the plating solution storage tank 22 is ejected upwardly from the bottom of the plating chamber 12 by the pump 24 and applied perpendicularly to the surface to be plated of the substrate W. In this manner, a plating current flows between the anode plate 16 and the substrate W, forming a plated film on the lower surface of the substrate W. At this time, an overflow of the plating solution 10 from the plating chamber 12 is retrieved by the plating solution reservoir 20, and flows therefrom into the plating solution storage tank 22 via the plating solution return pipe 30.
In the conventional cup type plating apparatus, the jet of plating solution flows upwardly through pores or mesh of the anode plate 16 toward the lower surface of the substrate W. If the anode plate 16 comprises a soluble electrode, then peeled fragments of a black film attached to the surface of the anode plate 16 are carried by the plating solution to the lower surface of the substrate W. Those fragments of the black film tend to lower the quality of the plated film. In addition, the plating solution is liable to come into contact with cathode pins which supply an electric power to the substrate W, precipitating the plating metal. When the substrate W is subsequently removed, the plated layer near the cathode pins may possibly be damaged.
For electroplating the surface of a substrate with copper, since copper is likely to be diffused into silicon, a barrier layer of TiN, TaN, or the like is deposited on the surface of the substrate, and a thin copper seed layer deposited on the barrier layer is used as a cathode. However, because no barrier layer is formed on the back and edge of the substrate, it is necessary to prevent the plating solution containing copper from being attached to the back and edge of the substrate. In immersion plating, therefore, the substrate is held by a substrate holder, and the outer peripheral edge of the surface of the substrate is sealed by a seal member so as to prevent the outer peripheral edge and back of the substrate from being wetted by the plating solution. Cathode pins are held in contact with the surface of the substrate in a space which is defined by the substrate holder, the substrate, and the seal member and which is held out of contact with the plating solution.
If the above substrate holder is applied to the jet plating process, then since the periphery of the substrate holder projects downwardly from the lower surface of the substrate, an air layer is created below the surface of the substrate simply when the substrate held by the substrate holder is brought into contact with the plating solution. Therefore, a good plated film cannot be formed on the surface of the substrate.
As shown in FIG. 30A of the accompanying drawings, the barrier layer 5 is formed so as to extend from the surface of a substrate W to an edge E thereof in view of the substrate area utilization efficiency, and the copper seed layer 7 is formed on the surface of the barrier layer 5. If the copper seed layer 7 is deposited to a thickness of 100 nm, for example, by sputtering on the entire surface of the substrate W, then not only a thin copper seed layer is formed on the surface of the substrate W, but also a thin copper seed layer is formed on the edge E of the substrate W, as shown in FIG. 30B of the accompanying drawings. A copper layer 6 is formed on only the surface of the substrate W by sealing the outer peripheral edge of the surface of the substrate W so as not to apply the plating solution to the back of the substrate W, as shown in FIGS. 30A and 30B. Consequently, the thin copper seed layer remains deposited on the edge E and an area near the edge E. The remaining thin copper seed layer tends to be peeled off while the substrate W is being transported or subsequently treated after it has been plated or polished by the CMP process, resulting in cross contamination with copper.
When a plated copper film produced by copper sulfate electroplating is left to stand at room temperature, the plated copper film is annealed, and its resistivity is lowered. The gradient of the resistivity differs depending on the plating conditions, the chemical compositions, and the substrate conditions. The resistivity of the plated copper film is stabilized into a value close to that of a copper bulk when it is left to stand for a period of time ranging from 24 hours to 300 hours after being plated.
The reduction in the resistivity means that the crystal grain of the plated copper film gradually becomes coarse and its volume is reduced slightly. When the plated copper film is polished by the CMP process, the reduction in the volume of the plated copper film must have been stopped. Inasmuch as the period of time in which the reduction in the volume of the plated copper film is stopped differs depending on the plating conditions and the substrate conditions, the plated substrate needs to be left to stand until it is stabilized before the CMP process is performed on the plated substrate.
It is therefore an object of the present invention to provide a method of and an apparatus for plating a substrate according to a jet plating process while preventing the plated film quality from being lowered due to particles produced by a black film or the like even if a soluble anode is employed.
Another object of the present invention is to provide a method of and an apparatus for plating a substrate in a state free of air bubbles while preventing a plating solution from being attached to cathode pins and also preventing the edge and back of the substrate from being contaminated by a metal.
Still another object of the present invention is to provide a method of and an apparatus for plating a substrate such that a remaining copper layer can fully be removed from an edge of the substrate and an area close thereto. Thus, a copper layer is prevented from being peeled off to cause a cross contamination with copper while the plated substrate is being subsequently polished by a CMP process or transported. The plated substrate can subsequently be polished by the CMP process in a short period of time after the substrate is plated with copper.
According to an aspect of the present invention, there is provided an apparatus for plating a substrate, comprising a plating chamber for holding a plating solution, the plating chamber housing an anode that is immersible in the plating solution held by the plating chamber, a plating solution supply part for supplying the plating solution to the plating chamber from an external source, and a substrate holder for removably holding a substrate and positioning the substrate such that a surface to be plated of the substrate is held in contact with the plating solution. The plating chamber has a plating solution outlet defined in a bottom thereof for discharging a portion of the supplied plating solution out of the plating chamber while the substrate is plated.
Peeled fragments or particles of a black film formed on the anode are discharged together with the plating solution through the plating solution outlet out of the plating chamber, and hence are prevented from being carried and attached to the surface of the substrate to be plated. Other foreign matter attached and deposited on the anode is also prevented from being carried and attached to the surface of the plated film on the substrate.
According to another aspect of the present invention, there is provided an apparatus for plating a substrate, comprising a plating chamber for holding a plating solution. The plating chamber houses an anode that is immersible in the plating solution held by the plating chamber from an external source. A substrate holder removably holds a substrate and positions the substrate such that a surface of the substrate to be plated is held in contact with the plating solution, and the plating solution supply part comprises a plurality of supply members disposed on a side wall or bottom of the plating chamber.
The anode placed in the plating solution is prevented from being directly contacted by the jet of plating solution, and an upward bulge can be formed on the surface of the plating solution. The upward bulge on the surface of the plating solution is effective to remove air bubbles from below the surface to be plated of the substrate when the substrate and the plating solution are brought into contact with each other before the substrate is plated while being immersed in the plating solution.
The supply members are oriented toward a central axis of the plating chamber.
With the supply members being thus oriented, slow swirls are generated in the plating chamber, stabilizing the flow of the plating solution therein. The slow swirls cause the plating solution to flow in the outer circumferential region of the plating chamber, where the plating solution would be slowed down if only the jets were ejected. Thus, the plating solution speed distribution can be improved over the overall surface to be plated of the substrate. In order to rotate the plating solution while forming the upward bulge on the surface of the plating solution, the direction of the jet should pass through a position spaced from the central axis of the plating chamber by a distance smaller than xc2xd of the radius of the substrate.
The apparatus further comprises a structure for discharging a portion of the supplied plating solution out of the plating chamber through the bottom of the plating chamber.
With the above discharging means, peeled fragments or particles of a black film formed on the anode are discharged together with the plating solution through the plating solution outlet out of the plating chamber, and hence are prevented from being carried and attached to the surface to be plated of the substrate. Other foreign matter attached and deposited on the anode is also prevented from being carried and attached to the surface of the plated film on the substrate.
According to still another aspect of the present invention, there is provided an apparatus for plating a substrate, comprising a plating chamber for holding a plating solution. The plating chamber houses an anode that is immersible in the plating solution held by the plating chamber, and a plating solution supply part supplies the plating solution to the plating chamber from an external source. A substrate holder removably holds a substrate and positions the substrate such that a surface to be plated of the substrate is held in contact with the plating solution. The substrate holder has a vent hole defined in a lower end thereof for removing air bubbles trapped below the surface of the substrate to be plated.
In order to reduce air bubbles trapped by the surface of the substrate to be plated, an outer circumferential portion of the substrate holder which is positioned below the substrate should be as thin as possible. However, because the substrate needs to be sealed in the substrate holder and also needs to be held in close contact with cathode pins in the substrate holder, it is difficult to reduce the thickness of the outer circumferential portion of the substrate holder which is positioned below the substrate, to less than several millimeters. The vent hole defined in the lower end of the substrate holder is effective to remove air bubbles trapped below the surface to be plated of the substrate and hence to prevent air bubbles from being trapped below the surface to be plated of the substrate.
Since a seal member and the cathode pins are disposed on the outer circumferential portion of the substrate holder which is positioned below the substrate, the vent hole cannot be positioned at the same height as the surface to be plated of the substrate. Consequently, the vent hole alone is unable to fully remove air bubbles trapped below the surface to be plated of the substrate. However, when the substrate holder and the substrate are rotated, the flow of the plating solution oriented radially outwardly from the center of the substrate is strengthened to force air bubbles trapped below the surface of the substrate to be plated out of the substrate holder.
According to yet another aspect of the present invention, there is provided an apparatus for plating a substrate, comprising a plating chamber for holding a plating solution. The plating chamber houses an anode that is immersible in the plating solution held by the plating chamber, and a plating solution supply part supplies the plating solution to the plating chamber from an external source. A substrate holder removably holds a substrate and positions the substrate such that a surface to be plated of the substrate is held in contact with the plating solution. An actuator has a rotating mechanism for rotating the substrate holder, and a lifting and lowering mechanism lifts and lowers the substrate holder. A cathode supplies electric power to the substrate, and the cathode does not come in contact with the plating solution.
In the above apparatus, the surface of the substrate to be plated is plated when the substrate holder is lowered by the lifting and lowering mechanism. The substrate is attached to or removed from the substrate holder when the substrate holder is lifted by the lifting and lowering mechanism.
When the substrate held by the substrate holder is lowered while being rotated horizontally, the surface to be plated of the substrate is brought into contact with an upward jet of plating solution in the plating solution in the plating chamber. The area of contact between the substrate and the plating solution is progressively spread outwardly, and at the same time, air bubbles trapped below the surface to be plated of the substrate are discharged from the substrate holder under centrifugal forces upon rotation of the substrate.
According to yet another aspect of the present invention, there is provided an apparatus for plating a substrate, comprising a plating chamber for holding a plating solution. The plating chamber houses an anode that is immersible in the plating solution held by the plating chamber, and a plating solution supply part supplies the plating solution to the plating chamber from an external source. A substrate holder removably holds a substrate and positions the substrate such that a surface of the substrate to be plated is held in contact with the plating solution. A rotating mechanism rotates the substrate holder, and a plating solution draining part discharges a portion of the plating solution out of the plating chamber thereby to lower the surface of the plating solution in the plating chamber, so that the substrate is exposed above the plating solution.
While the substrate held by the substrate holder is rotating, the surface of the plating solution is raised with an upward jet of plating solution being formed in the plating solution. As the surface to be plated of the substrate is brought into contact with the upward jet of plating solution, the area of contact between the substrate and the plating solution is progressively spread outwardly. At the same time, air bubbles trapped below the surface of the substrate to be plated are discharged from the substrate holder under centrifugal forces upon rotation of the substrate.
According to a further aspect of the present invention, there is provided a plating facility comprising a plating unit for plating a surface of a substrate having interconnection grooves and holes defined therein. An etching unit etches away, with a chemical solution, a seed film and/or a thin plated film on an outer circumferential edge of the substrate after the substrate is plated by the plating unit.
With the above arrangement, a seed film and/or a thin plated film on the outer circumferential edge of the substrate after the substrate is plated by the plating unit can be removed. Therefore, the substrate is free of a cross contamination with copper due to the film being peeled off while the plated substrate is being subsequently polished by a CMP process or transported.
The etching unit has a cleaning mechanism for simultaneously cleaning opposite surfaces of the substrate.
After the plated film is etched away from the outer circumferential edge of the substrate, the opposite surfaces of the substrate are simultaneously cleaned to remove plated film residuals that are etched.
According to a still further aspect of the present invention, there is provided a plating facility comprising a plating unit for plating a surface of a substrate having interconnection grooves and holes defined therein. A cleaning unit cleans the substrate after the substrate is plated by the plating unit, and an annealing unit heats the substrate thereby to anneal the substrate after the substrate is cleaned by the cleaning unit.
The substrate which has been plated by the plating unit and then cleaned by the cleaning unit is forcibly annealed by being heated by the heating unit. Therefore, the substrate can be polished by a CMP process without having to be left to stand until the plated film is stabilized.
The above plating facility further comprises an etching unit disposed between the plating unit and the cleaning unit, for etching away, with a chemical solution, a seed film and/or a thin plated film on an outer circumferential edge of the substrate after the substrate is plated by the plating unit. The annealing unit comprises means for annealing one substrate at a time.
According to a yet further aspect of the present invention, there is provided a method for plating a substrate, comprising the steps of producing a jet of plating solution in a plating solution contained in a plating chamber. The surface of the plating solution is brought into contact with a surface to be plated of a substrate held by a substrate holder, for thereby plating the substrate, and a portion of the plating solution is discharged out of the plating chamber.
According to still a further aspect of the present invention, there is provided a method of plating a substrate, comprising the steps of producing a jet of plating solution in a plating solution contained in a plating chamber. The surface of the plating solution is brought into contact with a surface to be plated of a substrate held by a substrate holder, and the substrate is rotated and the relative positions of the substrate and the plating solution are changed until the substrate is immersed in the plating solution, thereby to place the substrate in the plating solution.
The above method further comprises the step of lowering the substrate at a speed of at most 30 mm/second after the surface to be plated of the substrate has contacted the surface of the plating solution. The above step provides a sufficient period of time to discharge air bubbles trapped below the surface of the substrate to be plated out of the substrate holder.
The above method further comprises the steps of increasing the amount of the jet of plating solution until the surface to be plated of the substrate contacts the surface of the plating solution. The amount of the jet of plating solution is reduced after the surface to be plated of the substrate has contacted the surface of the plating solution. The above steps are effective to intensify an upward bulge on the surface of the plating solution until the surface to be plated of the substrate contacts the surface of the plating solution. If the jet of plating solution is too strong, then it tends to de-stabilize a black film formed on an anode, increasing peeled fragments or particles of the black film. Therefore, the amount of the jet of plating solution is reduced to a suitable level.
The above method further comprises the steps of exposing the substrate and the substrate holder above the surface of the plating solution after the substrate has been plated in the plating solution, and rotating the substrate holder at a speed of at least 500 rotations per minute to spin off the plating solution from the substrate. Since the substrate held by the substrate holder is rotated at the high speed, it can spin off the remaining plating solution. Thereafter, the substrate can be delivered to a next process by a robot arm or the like.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.